Concluding remarks

In summary, the vibrational modes were found to be between 99 and 95 $\%$ of the observed data. The errors were found to increase for the defects with fewer hydrogen atoms. Using this trend we predict that the VH defect will possess an A₁ mode at around 1885 cm^-1.

The infrared active stretch modes for V₂H₆ are found at higher frequency than those in VH₃ by a modest amount (< 2$\%$). We expect the stretch modes VH₃^- to be shifted upwards in frequency with respect to neutral VH₃. The Kohn-Sham levels show a similar pattern to that found in silicon : the addition of hydrogen atoms acts to move the defect levels from the gap. All the calculated acceptor and donor levels are predicted to lie in the lower half of the bandgap. The calculated adiabatic barrier for the reorientation of VH₃ is somewhat larger than the observed barrier in silicon (87 meV). We therefore propose that the movement of the hydrogen atom across the VH₃ defect is effected by tunneling from an excited state similar that described for the reorientation of O₂^- in KI[#!silsbee!#].